Almost all living organisms on the earth internally have “biological clock” that autonomously oscillates with a cycle of approximately 24 hours. The biological clock is thought to cause biological circadian fluctuation referred to as a circadian rhythm to govern circadian fluctuation of various biological phenomena (activity), including a living organism sleep-wake cycle, body temperature, blood pressure, hormonal secretion, metabolism, and also mental and physical activity, and eating. Circadian rhythm disturbance has been recently pointed out as a factor of various mental and physical symptoms or disease onset, such as sleep disorder, a skin disease, a lifestyle-related disease, and also neuropsychiatric disorder including depression.
The biological clock is controlled by a rhythm-generating system including a gene cluster referred to as “clock gene.” In the case of mammals, a feedback loop formed of promotion/suppression of transcription of a gene that codes four core proteins, CLOCK, BMAL, PERIOD and CRYPTOCHROME, is thought to form a core of a clock molecular mechanism, and if genes related to these core loops are not well expressed, to cause various diseases, including depression and a lifestyle-related disease (Non-Patent Literature 1).
A circadian rhythm control center (central clock) exists in a suprachiasmatic nucleus of hypothalamus. However, the clock gene has become clear to be expressed also in a peripheral tissue to form the circadian rhythm in a similar system. The clock gene is expressed also in skin, and in a manner similar to other organs, the clock gene beats out a rhythm in synchronization with a circadian rhythm center in a brain to maintain homeostasis (Non-Patent Literature 2).
For example, skin atrophy or suppression of body hair reproduction is seen in a BMAL1 knockdown animal, and if the clock gene does not satisfactorily work, skin health is adversely affected (Non-Patent Literature 3).
Hyaluronic acid is one kind of glycosaminoglycan, and widely exists in a living body, including a joint. Hyaluronic acid exists also in skin and is related to skin moistening and flexibility. Further, hyaluronic acid in skin is reported to be metabolized in a unit of approximately one day, and this quick metabolism is reported to contribute to keeping of good skin health by removal of a hazardous substance or the like (Non-Patent Literature 4).
For example, Patent Literature 1 describes that a strawberry seed extract promotes expression of a hyaluronic acid synthase gene or the like to have moistening action and skin-beautifying action.